1. Field of the Invention
The present invention concerns a device for the monitoring of ice formation, using a source of radiation that emits rays continuously, with a radiation sensitive installation that responds to incident rays and produces an electrical output signal and with a transparent element that is placed between the one source of radiation and the radiation sensitive installation and whose transparency changes depending on the condition of its surface.
2. Description of the Prior Art
Undesired formation of ice the surfaces of machines or installations--caused by conditions in the environment or of the operation--can have a negative influence on their operation or even damage them. This is especially true with heat regenerators where the flow canals can be narrowed by ice formation or with aircrafts where the weight can be increased to an intolerable degree by ice formation on the skin or where the rudder could be blocked. Especially endangered are the intakes of axial compressors which take in air of varying humidity and of varying temperature, depending on variations in the atmospheric conditions, and where, in the case of ice formation, the pressure distribution in the subsequent compressor steps could be influenced in an unplanned manner and which could be damaged if ice accumulation would cause an imbalance of the rotor or if ice pieces would separate from the rotating blades and were thrown against other parts of the engine.
For this reason there are already several devices known that monitor the ice formation on surfaces.
A first one of the known devices contains a plug mounted on a support plate that reaches into the area to be monitored or is installed adjoining to that area. With the aid of an electrical device, this plug is made to vibrate. The frequency of these vibrations depends on the degree of cleanliness of the surface of this plug, which means that when it starts to ice up the frequency changes. As soon as the measured change in frequency reaches a certain level, a warning signal is activated. The device has the disadvantage that there is no difference detectable between icing up and the accumulation of dirt, for example dust, which restricts the practical application considerably.
Other known devices work on the principle of a light barrier with a mirror set into the light path between the light source and the light receiver. When humidity condenses or ice forms on the mirror, its reflection capabilities are reduced which causes a corresponding change in the output signal of the light receiver. Because of the optical transparency and the good optical reflection by thin ice layers, the indicator sensitivity is relatively slight, especially during the early stages of ice formation. In addition to this, this installation also cannot distinguish between ice formation and the accumulation of dirt.